1. Field of the Invention
The present invention relates in general to commutators for motors wherein the commutator has a roughened surface. The invention also relates to the method of manufacturing the commutator according to the invention.
2. Description of the Prior Art
Motor commutators according to the prior art utilize oil which is applied to the commutator so as to prevent the generation of fine arcs due to the contact and separation of the brushes to the commutator segments. Such arcing causes surface changes due to oxidation, sulfidation of the contact surface during operation. When oil is coated on the commutator and a thin oil film will be present on the contact surface between the commutator segments and the brush which causes the electrical contact to be deteriorated and disturbed. In prior art commutators so as to avoid this defect fine concave-convex surfaces have been formed on the surfaces of each of the commutator segments with the concave portions acting as an oil tank while maintaining good electrical contact between the commutator segments and the brush. Generally, the concave-convex surfaces formed on the commutator segments are formed with sandpaper or an abrasive wheel which contacts the commutators surface as they are relatively rotated so as to abrade the surface of the commutator and the segments. Thus, the concave-convex surface on each of the commutator segments of the prior art commutators has been formed as a concave-convex line-shape pattern which extends along the rotational direction to the end and edge of each commutator segment. This results that burrs or fins are formed on the end edge of each commutator segment due to the rotational abrasion. When the motor is driven, the burrs peel off from the commutator segment and cause short circuiting between the commutator segments. Thus, in the prior art, it has been necessary to provide a step in the process of manufacturing so as to remove the burrs from the end edges of the commutator segments. With small motors such as micromotors such a deburring process must be carried out when using a microscope which is very tedious and time consuming and causes great fatigue to a worker which results in the production of such motors being slow and expensive.